Treatment of gelatin



Feb. 17,l 1942. E. E. JELLEY TREATMENT OF GELATIN Filed Sept. 25, 1959 INVENTOR BY f1 TTOR YS EDM/v5. ./ELL EY les@ khlv H l @SMQ l' Patented Feb. 17, 1942 TREATMENT OF GELATIN Edwin Ernest J elley, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application September 23, 1939, Serial No. 296,320 In Great Britain November 22, 1938 7 Claims.

This invention relates to the treatment of gelatin. It is known that gelatin nds many uses in technology and especially in the preparation of photographic products. Gelatin, being a natural product, is liable to considerable variation in some of its constituents, from batch to batch, even though the batches are of the same type of gelatin. These variations can, and frequently do, cause considerable variation in the behavior of the gelatin in practice.

In the preparation of gelatin to be used for photographic products, it is necessary to give the gelatin a special treatment or puriiication in order to remove substantially all of certain of the mineral matter occurring naturally in the gelatin. Particularly where the gelatin is to be used as a medium in which acid dyes, especially sulfonated dyes, are dispersed,` it is essential to substantially remove mineral matter, such as calcium from the gelatin, in order to avoid crystallization or precipitation of the dyes in the gelatin. In removing mineral matter, such as calcium, from gelatin intended for use in the preparation of photographic products, it is essential to avoid substantially any appreciable disturbance of the properties of the gelatin which make it a useful substance in the preparation of photographic products. Thus, it is essential to avoid substantially changing the pH of the gelatin and to avoid substantial removal of certain constituents which affect the sensitivity of the light-sensitive mate-` rials which may be introduced into the gelatin.

It is known that calcium can be substantially removed from gelatin by washing the gelatin with aqueous solutions of common salt (about 10% by weight, in strength) which solution contains hydrochloric acid. Repeated washings are necessary substantially to free the gelatin from calcium, the latter washings being carried out with with a neutral 1% salt solution, and the nal Washings with distilled water to remove the salt introduced into the gelatin by the initial washings. Such a method is obviously time-consuming and impractical for large scale treatments. This known process has the further great disadvantage of changing the pI-I of the gelatin considerably; a change which is vitally important to avoid, particularly where the gelatin is to be used as a vehicle for the incorporation of dyes, such as are customarily used in color photographic processes, light lters, and the like. Furthermore, treating gelatin according to this known process causes the gelatin to swell considerably so that it is diicult to avoid substantial losses during the several washings.

Accordingly, it is an object of my invention to provide an improved process for the treatment of gelatin whereby calcium is substantially removed from the gelatin in a manner easily applicable to large scale treatments and without appreciably disturbing the other properties of the gelatin. Other objects will appear hereinafter.

In accordance with my invention, I treat a solution of gelatin (advantageously an aqueous solution) with a base-exchanging alkali metal or ammonium zeolite. During the treatment, the calcium in the gelatin appears to be replaced by its equivalent of the base occurring in the zeolite, i. e. by sodium, potassium or ammonium, for example, the calcium taking the place of the alkali metal or ammonium in the zeolite. As base-exchanging zeolites, I have found that the synthetic Izeolites, such as are commercially employed as water softeners (permutite water softeners) are advantageously employed. As is well known, the base-*exchanging Zeolites are complex silicates which can probably .best be represented by the following general formula:

In this formula, M20y represents a basic oxide, such as sodium or potassium oxide, for example: R203 represents an amphoteric metal oxide, such as alumina or ferrie oxide, for example; SiOz represents two or more molecules of silica; and um() represents various amounts of water hydration. I do not intend that my invention be limited in any manner by the above formula, as I can employ any base-exchanging alkali metal or ammonium zeolite and the above formula is to be construed as only representative of the composition of base-exchanging zeolites in accordance with established custom.

In carrying out my new process, it is advantageous to place the zeolite in a container in such a manner that a solution of gelatin can be circulated through the container and in contact with the zeolite. It is then merely necessary to circulatethe gelatin solution over the zeolite until the gelatin solution no longer gives a precipitate when treated with a solution of an oxalate, such as sodium oXalate, for example. The absence ofl the precipitate, upon treatment of the soluble oxalate, of course, indicates the substantial removal of calcium ions from the gelatin solution.

Reference to the accompanying drawing will assist in understanding my invention. In the drawing, a practical arrangement for carrying out my new process is depicted diagrammatically.

According to the invention, gelatin is dissolved in water in a tank II] which is equipped with a stirring means II and a steam coil I2 for warming the water to facilitate solution of the gelatin. By means of the stirrer, solution can be further hastened. After a solution of the gelatin is prepared, the solution is driven by means of a pump I3 into either one of duplicate units Z and Z', Using the unit Z as an example, the gelatin solution passes through an open valve I4 (with the valve I4 to the unit Z closed) and into the bottom of a treating tank I5, where the solution rises, passing throughv a perforated basket I6 containing loosely packed granules of a zeolite, with the service valves I'I, I8 and I9 at the top of the treating tank closed and a pressure release valve 2U open to the atmosphere. After the gelatin solution has risen to the top of the treating tank, pumping is stopped and the valve I4 leading to the pump is closed. Upon opening a take-up valve 2| at the bottom of the treating tank, the gelatin solution containing gelatin substantially free from calcium flows out through an adaptor 22 where it is collected and concentrated in a manner well known to those skilled in the art, in order to obtain the substantially calcium-free gelatin. (See Gelatin in Photography, by S. E. Sheppard, D. Van Nostrand Co., New York, 1923.)

Should a test portion of the gelatin solution which is collected give a test for calcium ion with a soluble oxalate, it is, of course, necessary to put the solution through the treatment a second or even a third time. However, with suitable apparatus one treatment ordinarily sui'- ces to provide substantially calcium-free gelatin.

As the amount of gelatin solution treated increases, the zeolite granules gradually loose their potency. To revive the zeolite, the take-off valve 2l is closed and a waste valve 23 at the bottom of the treating tank is opened. Water is. then introduced at the top of the treating tank through the service valve I8. The water flows down over the zeolite granules removing occluded gelatin and passing out at the bottom of the treating tank through the waste valve and to a waste drain through the adapter 24. After the water is introduced (or preferably simu'ltaneously with the introduction of the water), steam is introduced at the top of the treating tank through the steam service valve I'I. The steam serves to heat the water passing down over the zeolite granules, thereby facilitating removal of occluded gelatin. It is essential to steam the zeolite granules in some such manner, in order to remove occluded gelatin if the zeolite is to be revived satisfactorily. Following removal of the occluded gelatin, the water and steam are cut oi and a brine (sodium chloride solution of about strength) is introduced at the top of the treating tank through the brine service valve I9. The brine passes down over the zeolite granules,v reviving the zeolite (owing to replacement of calcium in the dissipated zeolite with sodium) and out through the waste valve 23 and the waste adaptor 24.

After allowing sulicient brine to pass down over the zeolite granules to revive them, the brine service valve is closed and the excess brine washed out with water. After Washing is completed the waste valve 23 is closed and the unit is ready for further treatment of gelatin solution. Instead of brine, any water soluble alkali metal or ammonium salt can be employed to revive the zeolite.

While the zeolite in the unit Z is being revived, gelatin solution can be treated in the other unit Z', thereby avoiding any necessity forga shut-down while reviving the zeolite. The two units Z and Z are replicas, so that a description of one suces for the other. Corresponding parts in the Z and Z units bear the same numerals, the numerals in the Z unit however being primed.

The parts of the apparatus with which either the treated or untreated gelatin solution come in contact are advantageously made of stainless steel or Monel metal, in order to avoid contamination of the gelatin with metals like iron or copper, since even small amounts of these metals (particularly iron) are undesirable in gelatin intended for use in photographic processes.

The size of the apparatus can be any convenient arrangement, although the greater the surface of zeolite available to come into contact with the gelatin solution, the better the likelihood of obtaining a gelatin solution substantially free from calcium with one circulation over the zeolite granules.

The smaller the zeolite granules the greater the surface exposed for contact with the gelatin solution. However, with very small granules, the granules pack together so closely that circulation through the pack is hindered. In practice, granules having an average diameter of from l to 5 mm. are satisfactory.

The concentration of the gelatin solution is advantageously equivalent to not more than about 20% by weight of gelatin. A concentration of about 10% works very well. In preparing the initial gelatin solution, distilled water or even a good common water can be employed. That is to say, it is not necessary to avoid waters containing calcium and magnosium salts, since the base-exchanging zeolite will (as is well known in the water-softening art) remove calcium and magnesium from the water,` in addition to removing the calcium from the gelatin as I have found.

Gelatin prepared in accordance with my invention is of particular value as a medium for the dispersion of dyes, e. g. chrysophenine, such Yas are used in filter layers or for incorporation in gelatino-silver-halide emulsions according to the Various needsof photography.

What I claim as my invention and desire to be secured by Letters Patent oi the United States is:

1. A process for removing calcium from gelatin comprising treating a solution of calciumcontaining-gelatin with a zeolite selected from the group consisting of base-exchanging alkali metal and ammonium Zeolites, until the calcium` is substantially removed from the gelatin,

2. A process for removing calcium from gelatin comprising treating an aqueous solution of calcium-containing-gelatin with a base-exchang ing zeolite selected from the group consisting oi base-exchanging alkali metal and ammonium Zeolites, until the calcium is substantially removed from the gelatin.

3. A process for removing calcium from gelatin comprising treating an aqueous solution of calciu -containinggelatin with a zeolite selected rom the group consisting of synthetic alkali metal and ammonium zeolites, until the consisting of base-exchanging alkali metal and 15 ammonium zeolites.

6. A process for removing calcium from gelatin comprising treating an aqueous solution of calcium-containing-gelatin with a base-exchanging sodium zeolite, until the calcium issubstantially removed from the gelatin.

'7. A process for removing calcium from gelatin comprising treating an aqueous solution containing from about ten percent to about twenty percent by Weight of calcium-containing-gelatin with a base-exchanging zeolite selected from the group consisting of base-exchanging alkali metal and ammonium zeolites, until the calcium is substantially removed from the gelatin.

EDWIN ERNEST JELLEY. 

